Production of methyl acetylene and magnesium alcoholates



Patented June 6, 1950 PRCDUCTION OF METHYL ACETYLENE AND MAGNESIUMALCOHOLATES v Alva C. Byrns, Los Altos, Calif assignor to KaiserAluminum & Chemical Corporation, a

corporation of Delaware No Drawing. Application April 7, 1945, I

Serial No. 587,205

Claims. 1

This invention relates to chemical processes involving the alcoholysisof. magnesium carbide.

Objects of this invention include the production by such alcoholysis ofmethyl acetylene and of various magnesium alcoholates, and other ob-vjects will be apparent on reading this specification.

' Difiiculties have been encountered in hydrolyzing magnesium carbide bymeans of either water or acid, and in fact, the difliculties haveincreased with increase in concentration of the acid. Difficulties havealso been met with in alkali hydrolysis. For instance, when water isused as the hydrolytic agent, reaction proceeds so energetically thatthe material may be heated to incandescence. There is the furtherdisadvantage that gelatinous magnesium hydroxide is produced whichprevents penetration of the hydrolyzing agent to the center of theparticle with consequent loss of yield. With acid, and even morenoticeably with alkali, hydrolysis, considerable hydrogenation of themethyl acetylene occurs due to traces of freeqmagnesium metal which areleft at the end of reaction.

According to this invention it has now been found that the above objectscan be attained and the above disadvantages largely avoided byhydrolyzing magnesium carbide by means of a substantially anhydrousalcohol. The presence of small amounts of alcoholate or hydrocarbon inthe alcohol is not objectionable.

The magnesium carbide, MgzCawhich is used in this reaction may be fromany available source. It is a stable carbide and its method ofpreparation as well as its characteristics and behavior are described inthe article on magnesium carbides by Rueggeberg, Jour. Am..Chem. Soc.,Vol. 65, 602-606 (1943). The magnesium carbide may be prepared forexample, by the reaction between magnesium metal and hydrocarbons atelevated temperatures, a range of about 1280 to 1320 F. being generallypreferred, with butane or pentane ordinarily being preferred as thehydrocarbon. Natural gas can also be used, as well as other hydrocarbongases. Some magnesium carbide corresponding to the formula MgCz isusually formed but at the temperatures indicated the proportion is verysmall. Some cracking of hydrocarbon occurs with the formation of acarbonaceous deposit, and some olefins may be formed. The MgzCa preparedas described always contains, therefore, some impurities, the majorproportion thereof being carbon, but the carbide content is usuallyabout 80%. Based upon the magnesium used the yield may be made toapproach 100%, so that the magnesium metal content of the product isbelow 1%. The presence of nitrogen causes some of the magnesium metal tobe converted into nitride. When this is not desired, the

' presence of nitrogen should be avoided. Howmethyl alcohol, liberatingammonia gas and giving a solution of magnesium methylate in the and thusmakes available magnesium values in a.

by-product of the manufacture .of magnesium metal. Such carbothermicdust results where a reaction mass including an oxygen compound ofmagnesium is caused to react with a reducing agent yielding vaporousproducts of reduction such as Mg and CO vapors, and the vapors issuingfrom the reduction zone are extremely rapidly chilled by means of ahydrocarbon gas or other inert chilling agent from a temperature abovethe dissociation point of any magnesium compound that could otherwise beformed, to a temperature at which the elemental magnesium will not reactto form a magnesium compound and will remain in the elemental form.Although specific sources of magnesium carbide MgzCa are referred to, itis to be emphasized that it may be obtained from any source thereof.

Methyl acetylene and magnesium methylatev are produced simultaneously byreacting, for example, one gram of the magnesiumcarbide MgzCs withthirty milliliters of commercial absolute methanol (methyl alcohol) inthe presence of one milliliter of carbon tetrachloride or similarorganic halide, such as chloroform, methylene dichloride, etc., whichactivates or catalyses the alcoholysis. The reaction proceeds at roomtemperature according to the following equation;

The methyl acetylene is a gas and the magnesium methylate is soluble inthe excess of methyl a1- cohol present, so that separation of the twoproducts is simple. The concentration of the magcontrolled by theproportions of such alcohol present an in this example amounts to aboutone mol. per liter at room temperature, or more at higher temperatures.The magnesium methylate is crystallized from the solution by chilling,for example to 32 F. or 0 C., with 3 to 4 mols. of methanol ofcrystallization present. The solution may be recycled when desired, andthe presence of some alcoholate in the alcohol for reaction is notdisadvantageous.

The proportions of materials used as given above are preferred and theycan be varied when it is desired to produce either or both of theproducts mentioned, but it is generally preferred that the amount ofcarbon tetrachloride or'other activator present does not exceed aboutfive percent. Other alcohols can be used in place of the methyl alcohol,with the production of the corresponding alcoholate and methyl acetylenein each instance, according to the general equation Mg2C3+4ROH=2Mg(OR)2+HCEC-CH3, where R designates an alcohol-forming radical. Methyl,ethyl, isopropyl alcohols, ethylene glycol and glycerine, and otheralcohols can be used for the alcoholysis of this invention.

Some of the magnesium alcoholates are not as soluble in thecorresponding alcohol as the methylate and some may be practicallyinsoluble, and this may result in the formation of an insoluble film ofmagnesium alcoholate on the surface of the magnesium carbide, which mayslow down or interfere with the progress of the reaction. The reactioncan then be generally made to progress by the presence of enough solventfor the magnesium alcoholate produced to dissolve it suftlciently topermit the reaction to proceed. Such solvent can be a suflicient excessof the alcohol used.

The alcoholysis reaction is somewhat similar to the hydrolysis reactionaccording to the equation MgzCa-l-2HzO=2MgO-l-HCECCH3' or the equation,if more water is present,

However, such use of water is unsatisfactory because the reaction is toovigorous, and it is even more vigorous if an acidic reagent is used. Thereaction mass becomes too hot under some conditions resulting inincandescence, causing decomposition of the magnesium carbide MgzCs andalso of the liberated methyl acetylene. The violence of the reaction canbe toned down by diluting the water used with alcohol, that is using analcohol containing only a small amount of water. The reaction proceedsas an alcoholysis reaction when anhydrous alcohols are used, for whichthe presence of a catalyst is generally desirable. The reaction of thecarbide or nitride with methyl alcohol is mild and easily controlled.and the same is generally true for other alcohols.

Magnesium alcoholates, as is true of magnesium methylate, generallyreact with any water present to yield magnesium hydroxide and thecorresponding alcohol; and when less water is present than is requiredto form the hydroxide, basic magnesium methylate is apparently formed,and this seems to be the case with respect to some other magnesiumalcoholates; so that the presence of water is to be avoided as much asis expedient when it is desired to produce magnesium alcoholate.

Magnesium methylate is useful as a dehydrating agent, particularly foralcohols as well as for other materials; for reaction with alkyl halidesto produce ethers; for reaction with fatty acids to produce thecorresponding magnesium soaps; for reaction with water to be hydrolysedthereby to produce a chemically pure or United States Pharmacopeia gradeof magnesium hydroxide: and for such other purposes as may be desired.The same is more or less generally true of other magnesium alcoholates.The magnesium hydroxide so prepared is very pure; and when calcinedyields magnesium oxide which not only is very pure but has exceedinglyhigh surface activity. The methyl acetylene is useful in making resinsand propionaldehyde and it has other uses as well, although it hashitherto been more or less of a laboratory curiosity.

The magnesium alcoholate may contain impurities, depending on impuritiespresent in the reagents used to make it. To purify it, the alco- 4holate may be dissolved in an excess of the corresponding alcohol, or inother solvent, with the application of heat where it is desired toproduce a more concentrated solution, the solution filtered off, and thesolute recovered by crystallization or by evaporation of the solvent. 1

A reaction of alcohol also occurs with the mag-' nesium carbide MgCz ,toproduce magnesium alcoholate and acetylene, according to the generalequation MgC2+2ROH=Mg (OR) 2+C2H2 where Rrepresents an alcohol-formingradical. This is of interest, for example, when working withcarbothermic dust which frequently con tains, beside MgaCa, anappreciable amount of MgCz. The mixture of acetylene and methylacetylene obtained in such a procedure can be treated to recover eachconstituent separately, when so desired. I

What is claimed is:

1. Thc process of making a magnesium alcoholate and methyl acetylene,which comprises the alcoholysis at room temperature of magnesium carbidecorresponding to the formula MgzC: with an alcohol which issubstantially anhydrous, in the presence of an organic halide catalyst.

2. The process of making magnesium methylate and methyl acetylene, whichcomprises the alcoholysis of magnesium carbide corresponding to theformula MgzCs with substantially anhydrous methyl alcohol in thepresence of a small amount of carbon tetrachloride as catalyst, to forma solution of magnesium methylate in methyl alco hol and gaseous methylacetylene.

3. The process of making magnesium methylate and methyl acetylene, whichcomprises the alcoholysis of about one gram of magnesium carbidecorresponding to the formula MgzCs with about thirty milliliters ofsubstantially anhydrous methyl alcohol in the presence of about onemilliliter of carbon tetrachloride, to form a solution of magnesiummethylate in methyl alcohol and gaseous methyl acetylene.

4. A process of making a magnesium alcoholate and methyl acetylene,which comprises the alcoholysis of magnesium carbide corresponding tothe formula MgzC: with an alcohol which is substantially anhydrous, inthe presence of an organic halide catalyst.

5. A process for making a magnesium alcoholate, which comprises reactingan alcohol with compounds selected from the group consisting ofmagnesium carbide, corresponding to the formula MgzCa, and magnesiumnitride, said reaction being carried out under substantially anhydrousconditions and in the presence of an organic halide catalyst.

ALVA C. BYRNS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 7 OTHER REFERENCES Zeitschrift fur PhysekalischeChemie, vol. 73, pages 513-528 (1910). (Article by Novak),

Co7ntardi "Chemical Abstracts, vol. 31, 4265 (193

5. A PROCESS FOR MAKING A MAGNESIUM ALCOHOLATE, WHICH COMPRISES REACTINGAN ALCOHOL WITH COMPOUNDS SELECTED FROM THE GROUP CONSISTING OFMAGNESIUM CARBIDE, CORRESPONDING TO THE FORMULA MG2C3, AND MAGNESIUMNITRIDE, SAID REACTION BEING CARRIED OUT UNDER SUBSTANTIALLY ANHYDROUSCONDITIONS AND IN THE PRESENCE OF AN ORGANIC HALIDE CATALYST.